Japanese Patent Application Laid-Open (JP-A) No. 2006-76558 discloses a flat cylindrical disc inflator mounted to a driver's seat airbag device. In this type of disc inflator, due to the operation of a squib (ignition device) disposed at an axial core portion, a gas generating agent filled at an outer peripheral portion of the squib combusts, and a large amount of gas is generated. The generated gas is ejected from plural gas ejection holes formed in a peripheral wall portion of an upper case, and flows into an airbag which is in a folded state.
Conventionally, in an inflator in which a gas generating agent combusts and gas is generated, in order to remove combustion residue created when the gas generating agent combusts (hereinafter also referred to as “mist”), and to cool a high temperature gas, a coolant filter wrapped in a ring shape is disposed at an inner peripheral portion of the upper case. As a result various problems have arisen, such as the need to enlarge the inflator in a radial direction, and to increase the weight of the inflator.
In order to address these issues, an inflator having a filterless structure in which a coolant filter is not used has been developed (see Japanese Utility Model Registration No. 3122258 and Japanese Utility Model Registration No. 3122259). A brief explanation of this technology is that, a gas generating agent is filled into a combustion chamber of an inflator, and a flow forming member that forms a gas flow path that is L-shaped in a longitudinal section is provided concentrically at an outer peripheral portion of the gas generating agent. According to this configuration, when the direction in which gas flows is changed, mist of the gas generating agent adheres to a wall surface and is removed, and the gas that flows into the airbag is also cooled.    Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 2006-76558    Patent Document 2: Japanese Utility Model Registration No. 3122258    Patent Document 3: Japanese Utility Model Registration No. 3122259    Patent Document 4: JP-A No. 2001-341610 (see FIGS. 1 and 5, and paragraph [0064])    Patent Document 5: JP-A No. 2007-508979